Soft Robotics Gets a Boost With Artificial Muscle

A soft gel filled with tiny bubbles may not look like much. But when it pulsates ultrasonic wavesThe material behaves like natural muscles: it compresses, grips and lifts with amazing strength.

Opening, reported this week in Natureintroduces a new type of artificial muscle that is not powered by wires, batteriesor shakes, but by sound.

The acoustic trick behind these bubble muscles opens the door to wireless control, rapid response, and even deep tissue targeting. This may lead to soft robots who with lively dexterity make their way through narrow places, surgical instruments which bend and curve within the body, or tender grips who can manipulate fragile objects without breaking them.

“From a medical point of view, this is really cool,” says Ryan Trubymaterials scientist Northwestern University who did not participate in the study. “They take relatively simple approaches but integrate them in new, smart ways.”

robotics the community has been trying to develop for a long time artificial muscles which rival living tissue in flexibility and elasticity. Motors And hydraulics can use force, but lacks dexterity and may pose a safety hazard inside the body, while soft drives– controlled by heat, air or chemical reactions – are usually bulky, inefficient or too slow for practical use.

Daniel Ahmednanorobotician in ETH Zurich took a different approach. Using the power of acoustic resonance, he and his colleagues placed thousands of microscopic bubbles in a soft, biocompatible gel, arranging the air sacs in lattice patterns so that they move when struck. Ultrasound.

Bubbles of different sizes respond to different frequencies of ultrasound, allowing you to control which parts of the material bend.ETH Zurich/Nature

By adjusting both the frequency of the ultrasound and the size of the bubbles in the muscle-mimicking arrays, the researchers allowed the gel to bend, rotate, or deform—essentially turning invisible vibrations into controlled movement. “By activating different sets of frequencies,” says Ahmed, “you can actually get programmable muscles.”

Several prototype devices demonstrate vesicular muscles in action.

In one demonstration, researchers created something similar to a claw. capture which snaps around living zebrafish larvae without damaging the delicate animals. In another, they built a ship in the shape of a stingray. soft robot whose fins, studded with tiny bubbles of three different sizes, vibrated under the influence of ultrasound, propelling it smoothly through the water – even in the stomach of a pig. (Not alive, in case you were wondering.)

Using pig tissue from a local slaughterhouse, Ahmed's team also demonstrated how the material could set. For example, a section of gel with a bubble pattern stuck tightly to the surface of a pig's heart and remained in place for more than an hour, bending under the influence of ultrasound.

A patch the size of a bandage is firmly glued to the outside of the pig's heart.ETH Zurich/Nature

In another experiment, researchers encased artificial muscle material in a biodegradable capsule and inserted it into a pig's bladder. Once the capsule dissolved, the ultrasound activated the device, causing it to unfold and lock onto the inner wall of the tissue—a hint at how such systems could one day be used for targeted treatments within the body.

“We could actually use our system as drug delivery patches,” says study co-author. Zhang Shiformer Ph.D. student in Ahmed's lab, now at Westlake University in Hangzhou, China. “It has really practical applications.”

One of the remarkable features of ultrasound-guided artificial muscles is that the microbubbles involved can be monitored using standard ultrasound imaging. And since trigger frequencies (1 to 100 kilohertz) are much lower than those used for clinical imaging (1 to 20 megahertz), these two functions do not interfere.

However, all demonstration concepts so far have been tested on dead tissue, and it remains to be seen how well the system works inside a living rat or pig, much less a human body, especially since bones and other irregularly shaped tissues can scatter and attenuate the ultrasound signal, and fluids flowing inside the body can interfere with controlled movement.

“You can't tell whether it really works or not without alive evidence,” says W. Hong Yeobioengineer in Georgia Tech who did not participate in the study. The system is also limited by the fact that prolonged actuation causes the bubbles to expand, destabilizing their function after about half an hour.

However, Yeo points to their tiny size and fast response as features that could make vesicular muscles particularly attractive for biomedical implants. “It’s eye-catching,” he says. “It’s very unique and makes sense.”